EIF2S1, also known as eIF2α, is the alpha subunit of the translation initiation factor eIF2 complex which catalyzes the first regulated step of protein synthesis initiation, promoting the binding of the initiator tRNA to 40S ribosomal subunits. The phosphorylation state of eIF2S1 controls the rate of tRNA translation. When eIF2α is not phosphorylated, translation occurs at a normal rate.